Dental prosthesis component and method for producing dental prosthesis component

ABSTRACT

Provided is a dental prosthesis component which is a member to configure a dental prosthesis provided with an artificial tooth root, which have high strength and a good esthetic property. The dental prosthesis component ( 12 ),( 13 ) to configure a dental prosthesis ( 10 ) provided with an artificial tooth root ( 12 ), which are made of Zr-14Nb alloy, wherein a surface layer containing ZrO 2  and having a thickness of less than 80 μm as a main ingredient is formed on the components, and the surface has a brightness of Gly 8.0 or more of the color sheets according to Practical Color Co-ordinate System 201.

TECHNICAL FIELD

The present invention relates to a dental prosthesis component such asan artificial tooth root (implant, fixture) or an abutment to be usedfor a dental prosthesis to repair defective sites in a tooth row by theartificial tooth root, and a method for producing the dental prosthesiscomponent.

BACKGROUND ART

A dental prosthesis provided with an artificial tooth root comprises: anartificial tooth root whose one end is to be embedded in a jawbone; anabutment to be disposed in a manner that one end thereof is fixated tothe artificial tooth root and the other end is projected into an oralcavity; and an artificial tooth crown disposed in a manner to cap aprojected end portion of the other end of the abutment to function as anartificial tooth.

Herein, since the abutment holds the artificial tooth root and theartificial crown by connecting them, it is considered that the abutmentneeds to have certain degrees and more of strength, durability, andcompatibility to a biological body. From such a viewpoint, titaniumalloy is often used as a material to make the abutment. However, sincetitanium alloy has a color similar to black, when the end portion of theabutment is capped by the artificial tooth crown, black color of theabutment is seen through the artificial tooth crown and therebysometimes the appearance is not favorable.

With respect to this, Patent Document 1 (Japanese Patent ApplicationLaid-Open (JP-A) No. 2010-046153) for example discloses a techniqueusing a ceramic such as zirconia as a material to make an abutment.According to this, it is considered that defects in appearance asmentioned above can be resolved by using a white ceramic.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the abutment made of a ceramic as mentioned above has problemsthat the abutment has low toughness by its nature and thus is easy to bebroken. Also, with regard to color, esthetic improvement is desired bymaking the color of the abutment even closer to the color of a naturaltooth. Further, not only the abutment but also the artificial tooth roothas same problems since a part of the artificial tooth root is sometimesobserved by appearance.

Accordingly, an object of the present invention is to provide a dentalprosthesis component which is a member to configure a dental prosthesisprovided with an artificial tooth root with high strength and a goodesthetic property.

Means for Solving the Problems

The present invention will be described below. In order to make thepresent invention easy to understand, reference numerals given in theaccompanying drawings are shown here in parentheses. However, thepresent invention is not limited to this.

The present invention solves the above problems by a dental prosthesiscomponent (12), (13) to configure a dental prosthesis (10) comprising anartificial tooth root (12), the dental prosthesis component are made ofZr-14Nb alloy, wherein a surface layer containing ZrO₂ as a mainingredient and having a thickness of less than 80 μm is formed on thedental prosthesis component, and the surface of the surface layer has abrightness of Gly 8.0 or more of the color sheets according to PracticalColor Co-ordinate System 201. Herein, in respect to brightness,“Practical Color Co-ordinate System 201” corresponds to the Munsellcolor system with the same basis.

A thickness of the surface layer of the dental prosthesis component ispreferably 20μm or more to less than 80 μm.

Also, in a method, for producing the dental prosthesis component(12),(13) described above to configure a dental prosthesis (10)comprising an artificial tooth root (12), it is preferable to include astep of oxidation treatment carried out to a member to be a dentalprosthesis component made of Zr-14Nb alloy. In the step, the oxidationtreatment is preferably carried out in an atmosphere of 4% or more to20% or less of the oxygen density and in any one of following conditionsof (1) to (3).

(1) 700° C. or more to less than 800° C., for 10 hours

(2) 800° C. or more to less than 850° C., for 1 hour or more to lessthan 2 hours

(3) 850° C. or more to less than 900° C., for 0.5 hours or more to lessthan 2 hours

Effects of the Invention

According to the present invention, it is possible to provide a dentalprosthesis component which is a member to configure a dental prosthesisprovided with an artificial tooth root with high strength and a goodesthetic property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a configuration of the dental prosthesis10.

FIG. 2 (a) is a graph showing an analysis of X-ray diffraction of thesurface layers, and FIG. 2 (b) is another graph showing an analysis ofX-ray diffraction of the surface layers.

FIG. 3 (a) is a graph showing measurements of thicknesses of the surfacelayers, and FIG. 3( b) is another graph showing measurements ofthicknesses of the surface layers.

FIG. 4 (a) is a photograph of the surface of the surface layer of No. 3,FIG. 4( b) is a photograph of the surface of the surface layer of No. 5,and FIG. 4 (c) is a photograph of the surface of the surface layer ofNo. 12.

FIG. 5 (a) is a cross-sectional photograph of the surface layer of No.5, FIG. 5( b) is a cross-sectional photograph of the surface layer ofNo. 6, FIG. 5( c) is a cross-sectional photograph of the surface layerof No. 7, and FIG. 5( d) is a cross-sectional photograph of the surfacelayer of No. 8.

FIG. 6 (a) is a cross-sectional photograph of the surface layer of No.1, FIG. 6( b) is a cross-sectional photograph of the surface layer ofNo. 5, FIG. 6( c) is a cross-sectional photograph of the surface layerof No. 12, and FIG. 6( d) is a cross-sectional photograph of the surfacelayer of No. 14.

FIG. 7 is a view showing surface color of sample made under eachcondition.

MODES FOR CARRYING OUT THE INVENTION

The functions and benefits of the present invention described above willbe apparent from the following aspects for carrying out the invention.Hereinafter, the present invention will be described based on theaspects shown in the drawings. However, the invention is not limited tothese aspects.

FIG. 1 is an exploded view schematically showing a configuration of thedental prosthesis 10 illustrating one aspect. The dental prosthesis 10has an artificial tooth crown 11, an artificial tooth root 12, and anabutment 13.

The artificial tooth crown 11 is a portion which actually compensatesfor a defective site in a tooth row. Accordingly, the artificial toothcrown 11 is in a shape modeled after a natural tooth in appearance, thusreproducing a shape and texture of the natural tooth. The artificialtooth crown 11 is formed in a container shape and configured in a mannerto insert the abutment 13 described below thereinside and connect withthe abutment at a receiving portion 11 a. As the artificial tooth crown,a known artificial tooth crown may be applied.

The artificial tooth root 12 is the dental prosthesis component of thepresent invention, also called an implant or a fixture, and is a memberto be embedded in an alveolar bone so as to adequately fixate the dentalprosthesis 10 in an oral cavity. A known form of an artificial toothroot may be applied to as the artificial tooth root 12.

The abutment 13 is also the dental prosthesis component of the presentinvention, a member to be disposed between the artificial tooth crown 11and the artificial tooth root 12 and connect these to hold theartificial tooth crown 11. More specifically, one end of the abutment 13is fixated in a manner to be inserted into a hole 12 a formed in theartificial tooth root 12, and the other end of the abutment 13 isfixated in a manner to be inserted into the artificial tooth crown 11and be fitted in the receiving portion 11 a. A known form of an abutmentmay be applied to as the abutment 13.

Various configurations for a connecting structure of an artificial toothroot and an abutment have been suggested. For example, there is aconfiguration in which a male screw is formed on an abutment and afemale screw is formed in a hole of an artificial tooth root to fixatethe abutment and the artificial tooth root by screwing the screwstogether, or a configuration in which an abutment and an artificialtooth root are fixated by different screws. The configurations mentionedabove may be applied to the present invention without particularlimitations.

The artificial tooth root 12 and/or the abutment 13 as the dentalprosthesis component are formed of Zr-14Nb alloy, and has a surfacelayer containing ZrO₂ as a main ingredient and having a thickness ofless than 80 μm on the surface. Herein, the “main ingredient” refers tothe ingredient accounting for 50% or more of the total ingredientscomposing of this layer. Measurement of the thickness of the layer maybe carried out by a known method without particular limitations. Sincethe thickness of the surface layer is substantially even, the thicknessof the surface layer may be measured by taking photographs of some partof the surface layer by SEM and the like for example. According to this,cracking in the surface layer can be prevented. Herein, “no cracking”refers that it can be observed there is no cracking occurred in the SEMimage at 1000 fold magnification of the cross section of the surfacelayer. Also, the thickness of the surface layer is preferably 20 μm ormore. This makes it possible to adequately secure the thickness of thesurface layer thereby prevents even certainly the surface of the dentalprosthesis component from becoming parti-colored.

Also, the dental prosthesis component is made to have the same orsimilar color as that of the artificial tooth crown by forming thesurface layer. That is, white or a color similar to white. Preferably,the color of the surface of the surface layer is white which has abrightness of Gly 8.0 or more of the color sheets according to PracticalColor Co-ordinate System 201.

According to the dental prosthesis component as described above, thetoughness (that is, strength) becomes excelled, and the color becomescloser to the color of a natural tooth. This makes it possible toprovide dental prosthesis component having excellent durability with agood esthetic property, which can endure a long-time usage.

Next, a method for producing the dental prosthesis component accordingto one aspect will be described. The method for producing the dentalprosthesis component includes: a preparing step of a button-shaped ingotmade of Zr-14Nb alloy; a molding-cutting step; a processing step; and anoxidation treatment step.

The preparing step of the button-shaped ingot made of Zr-14Nb alloy(hereinafter, sometimes referred to as “step S1”) is a step to melt ahigh-purity Zr (purity of 99.6% by mass for example) and a high-purityNb (purity of 99.9% by mass for example) in a proportion which can formZr-14Nb and solidifying the resultant. A known method may be applied tothis step, and the melting and solidification may be repeated more thanonce in order to improve the homogeneity.

The molding-cutting step (hereinafter sometimes referred to as “stepS2”) is a step to melt the ingot obtained in the step S1, then obtainZr-14Nb in the shape of a rod by molding, and cut the rod in apredetermined size. The predetermined size is a size as a startingmaterial which can be applied to a cutting machine in the processingstep described below.

The processing step (hereinafter sometimes referred to as “step S3”) isa step of disposing the starting material obtained in the step S2 to aprocessing machine and cutting it to form a shape of the dentalprosthesis component. A NC machine tool based on a dental CAD/CAM systemcan be applied for cutting the material as an example. Also, polishingmay be carried out after the cutting.

The oxidation treatment step (hereinafter sometimes referred to as “stepS4”) is a step to form the surface layer described above containing ZrO₂as a main ingredient by carrying out oxidation treatment to the memberhaving the shape of the dental prosthesis component obtained by the stepS3. Conditions to form the surface layer are as below. Under the airatmosphere (that is, the oxygen density is about 20%), the material isexposed to a condition satisfying anyone of the following conditions of(1) to (3), setting treatment temperature and treatment time:

(1) 700° C. or more to less than 800° C., for 10 hours

(2) 800° C. or more to less than 850° C., for 1 hour or more to lessthan 2 hours

(3) 850° C. or more to less than 900° C., for 30 minutes or more to lessthan 2 hours

By the above, the surface layer as described above can be obtained. Theoxygen density does not necessarily need to be 20%, but preferably 4% to20%, and the oxidation treatment may be carried out in an atmospherewith such an oxygen density.

Examples

In examples, the treatment temperature and the treatment time in theoxidation treatment step described above were changed, and the ZrO₂layer formed in each case was examined. The treatments were carried outunder the air atmosphere. Therefore, the oxidation density wasapproximately 20%. Samples used were disk-shaped Zr-14Nb of 10 mm indiameter. The conditions and the results are shown in Table 1. Here,“time (h)” is a holding time after reaching the treatment temperature(aimed temperature).

In the results, “Thickness” was measured by the cross-sectionalphotographs by SEM, and “◯” was given if the thickness of the surfacelayer was less than 80 μm, and “X” was given if the thickness of thesurface layer was 80 μm or more. This is because, as described below,when the surface layer has a thickness of 80 μm or more, cracks increasein the surface layer, which increases a possibility of raising a problemin strength.

“Crack” was the results of evaluation according to degrees of the cracksin the surface layer. In the image of 1000 fold magnification of thesurface layer by SEM, “◯” was given if a crack was not found, and “X”was given if a crack was found.

“Color” was the evaluation of the surface colors of the samples, and “◯”was given if the color had a brightness of Gly 8.0 or more of the colorsheets according to Practical Color Co-ordinate System 201, and “X” wasgiven if the color had a brightness below Gly 8.0 of the same.

TABLE 1 Conditions Results (ZrO₂layer) No Temperature (° C.) Time (h)Thickness Crack Color 1 600 0.5 ◯ ◯ X 2 600 10 ◯ ◯ X 3 700 0.5 ◯ ◯ X 4700 10 ◯ ◯ ◯ 5 800 0.5 ◯ ◯ X 6 800 1 ◯ ◯ ◯ 7 800 2 X X ◯ 8 800 3 X X ◯ 9850 0.5 ◯ ◯ ◯ 10 850 1 ◯ ◯ ◯ 11 850 2 X X ◯ 12 900 0.5 X X ◯ 13 900 1 XX ◯ 14 1000 0.5 X X ◯

As shown in Table 1, in each of No. 1 to No. 6, No. 9, and No. 10, thethickness of the surface layer (ZrO₂ layer) was less than 80 μm and acrack was not created. Further, in each of No. 4, No. 6, No. 9, and No.10, it is possible to obtain a dental prosthesis component comprising asurface layer which is especially excelled in strength and has a goodesthetic property with a desirable color.

On the other hand, in each of No. 1 to No. 3 and No. 5, there was aproblem of color. The thickness of the surface layer was less than 20 μmrespectively.

In each of No. 11 to No. 14, although the color was desirable, thethickness was 80 μm or more, as a result cracks were created in thesurface layer and there was a problem of toughness (strength).

The above results will be described with examples below.

<Ingredients of the Surface Layer>

The ingredients of each of the surface layers were examined. The resultsis shown in FIG. 2( a) and FIG. 2( b). In both of FIG. 2( a) and FIG. 2(b), the horizontal axis represents 2θ, and the vertical axis representsstrength. Treatment temperature and treatment time are respectivelyshown to each line.

As seen from FIG. 2( a) and FIG. 2( b), it is considered that ZrO₂monoclinic is contained in majority in each case. And a slight amount ofZrO₂ in other crystal structure was also contained. On the other hand,NbO and Nbo₂ were hardly detected.

<Thickness of the Surface Layer>

The thickness of the surface layers was examined based on thecross-sectional photographs of the surface layers by SEM. FIG. 3( a) isa graph of the examples with the treatment temperature of 800° C., andwith each treatment time being changed. FIG. 3( b) is a graph of theexamples with the treatment time of 0.5 h, and with each treatmenttemperature being changed. The horizontal axis of each graph representsconditions and the numbers corresponding to Table 1, and the verticalaxis represents the thickness of the surface layers.

As seen from FIG. 3( a) and FIG. 3 (b), there is a tendency that thehigher temperature and the longer treatment time make the thickersurface layers, and No. 7, No. 8, No. 12, and No. 14 have thicknesses of80 μm or more.

<Cracks in the Surface Layers>

The cracks created in the surface layers were observed by SEM. FIG. 4(a), FIG. 4( b), and FIG. 4( c) show images of the surface layers by SEMtaken from the surface (at 1000 fold magnification). Treatmentconditions and numbers corresponding to Table 1 are shown to eachfigure. As seen from the figures, no cracks were created in No. 3 andNo. 5, but cracks were created in the surface layer of example No. 12.

Also, in FIG. 5 and FIG. 6, the images of the cross-sectional surfacesof the surface layers taken by SEM were shown. FIG. 5( a) to FIG. 5( d)are examples in which the treatment temperature was 800° C. and eachtreatment time was changed respectively. FIG. 6( a) to FIG. 6( d) areexamples in which the treatment time was 0.5 h and each treatmenttemperature was changed respectively. Each of the treatment conditionsand the numbers corresponding to Table 1 were shown in each figure.

As seen from these figures, cracks were created if the thickness of thesurface layer was 80 μm or more (No. 7, No. 8, No. 12 and No. 14).

<Color>

In FIG. 7, examples were shown in which the surface colors of thesamples were compared. Each of the treatment conditions and the numberscorresponding to Table 1 were shown with each example. As seen from FIG.7, in view of the treatment time and the treatment temperature, it isfound that if the surface layer becomes thin, a mottling shows up on thesurface. Therefore, the mottling is sometimes noticeable depending onthe conditions such as size, shape and the like of the samples.

DESCRIPTION OF THE REFERENCE NUMERALS

-   10 dental prosthesis-   11 artificial tooth crown-   12 artificial tooth root (dental prosthesis component)-   13 abutment (dental prosthesis component)

1. A dental prosthesis component to configure a dental prosthesisprovided with an artificial tooth root, the dental prosthesis componentis made of Zr-14Nb alloy, wherein a surface layer containing ZrO₂ as amain ingredient and having a thickness of less than 80 μm is formed onthe dental prosthesis component, and the surface of the surface layerhas a brightness of Gly 8.0 or more of the color sheets according toPractical Color Co-ordinate System
 201. 2. The dental prosthesiscomponent according to claim 1, wherein said surface layer has athickness of 20 μm or more to less than 80 μm.
 3. A method for producinga dental prosthesis component to configure a dental prosthesis providedwith an artificial tooth root, the method includes a step of oxidationtreatment carried out to a member to be the dental prosthesis componentmade of Zr-14Nb alloy, wherein the oxidation treatment is carried out inan atmosphere of 4% or more to 20% or less of the oxygen density and inany one of following conditions of (1) to (3). (1) 700° C. or more toless than 800° C., for 10 hours (2) 800° C. or more to less than 850°C., for 1 hour or more to less than 2 hours (3) 850° C. or more to lessthan 900° C., for 0.5 hours or more to less than 2 hours